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From "Erick Erickson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-6482) Add an onlyIfDown flag for DELETEREPLICA collections API command
Date Tue, 16 Sep 2014 18:25:34 GMT

    [ https://issues.apache.org/jira/browse/SOLR-6482?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14135890#comment-14135890
] 

Erick Erickson commented on SOLR-6482:
--------------------------------------

@Shalin:

bq: Why would anyone invoke DELETEREPLICA against a replica if they don't want it to be removed
from cluster state?

It's really the opposite, something of a safety valve. It's a situation where you _only_ want
to affect the cluster state, you do _not_ want to actually delete a replica if it's live.
Particularly for cleanup when a machine has died and it's never coming back.

I'm looking at it as a paranoia flag for DELETEREPLICA that expresses "if I screwed up and
called this on a live replica, ignore the command". Operationally, it's scary to turn a script
loose for maintenance that may, through a programming error or whatever, delete all the nodes
on my system.

One can argue that all this can be done by examining the cluster state and issuing the delete
replica only for nodes that are down and not need to add a flag to DELETEREPLICA and I suppose
that's true. But operations folks would like this kind of safety valve.

I'm not quite sure how this plays out in the ZK being "the one source of truth" model, when
we get there it may be irrelevant. But we're not there yet, it's completely optional, and
if omitted the behavior is the same as now so it's not a big change.


> Add an onlyIfDown flag for DELETEREPLICA collections API command
> ----------------------------------------------------------------
>
>                 Key: SOLR-6482
>                 URL: https://issues.apache.org/jira/browse/SOLR-6482
>             Project: Solr
>          Issue Type: Improvement
>          Components: SolrCloud
>    Affects Versions: 4.11, 5.0
>            Reporter: Erick Erickson
>            Assignee: Erick Erickson
>            Priority: Minor
>         Attachments: SOLR-6482.patch, SOLR-6482.patch, SOLR-6482.patch
>
>
> Having the DELETEREPLICA delete the index is scary for some situations, especially ones
in which the operations people are taking more explicit control of the topology of their cluster.
As we move towards ZK being the "one source of truth" and deleting replicas that then come
back up, this is even scarier.
> I propose to have an optional flag onlyIfDown that remove the replica from the ZK cluster
state if (and only if) the node was offline. Default value: false.



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